The present invention relates to a technique for intentionally degrading tone reproducing digital data, such as those of the MIDI (Musical Instrument Digital Interface) format, to cope with unauthorized use of the digital data when the digital data are transmitted via a wireless or wired transmission path, reproduced or copied.
To date, there have been developed various systems which allow tone reproducing digital data, such as those of the MIDI format, to be downloaded, via communication networks like the Internet, from servers to portable phones, personal computers, karaoke devices, etc. Generally, in these systems, data providers etc., each including a server computer, present users with charges for tone reproducing digital data to be provided, and tone reproducing digital data are delivered or sold from the server to a user terminal that has paid a predetermined charge.
Further, by virtue of short-range communication techniques known today, such as the “IrDA” and “Bluetooth” techniques, tone reproducing digital data, such as those of incoming-call signaling melodies (ring melodies), can also be communicated directly between portable phones without intervention of a server. Such tone reproducing digital data can be transmitted with an almost 100% reproducibility because of the digital nature. Thus, if the tone reproducing digital data are communicated between portable phones, the data, practically equal in data quality to the corresponding chargeable regular content sold through a regular route, may be copied free of charge. Therefore, in such cases, the data provider is unable to collect the charge for the tone reproducing digital data, which can be very great damage to the data providers. Further, copying of the tone reproducing digital data free of charge may constitute infringement on the copyright of the data.